Pass Physical Web metadata through a struct

ios/chrome/browser/physical_web/ios_chrome_physical_web_data_source.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/physical_web/ios_chrome_physical_web_data_source.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/values.h"
 #import "ios/chrome/browser/physical_web/physical_web_initial_state_recorder.h"
 #import "ios/chrome/common/physical_web/physical_web_scanner.h"
@@ skipping 34 matching lines @@
   scanner_.reset();
 }
 
 std::unique_ptr<base::ListValue> IOSChromePhysicalWebDataSource::GetMetadata() {
   if (!scanner_) {
     return base::MakeUnique<base::ListValue>();
   }
   return [scanner_ metadata];
 }
 
+std::unique_ptr<MetadataList>

[mattreynolds, 2017/01/11 20:54:50]

physical_web:: (here and in the MakeUnique call below)

[cco3, 2017/01/11 22:51:02]

Done.

+IOSChromePhysicalWebDataSource::GetMetadataList() {
+  if (!scanner_) {
+    return base::MakeUnique<MetadataList>();
+  }
+  return [scanner_ metadataList];
+}
+
 bool IOSChromePhysicalWebDataSource::HasUnresolvedDiscoveries() {
   return [scanner_ unresolvedBeaconsCount] > 0;
 }